1. Field of Use
The present invention relates generally to the field of antennas. More particularly, the present invention concerns evanescent coupling antennas. Specifically, a preferred embodiment of the present invention is directed to an evanescent coupling scanning antenna. The present invention thus relates to antennas of the type that can be termed evanescent coupling scanning antennas.
2. Description of Related Art
Within this application several publications are referenced by arabic numerals within parentheses. Full citations for these, and other, publications may be found at the end of the specification immediately preceding the claims. The disclosures of all these publications in their entireties are hereby expressly incorporated by reference into the present application for the purposes of indicating the background of the invention and illustrating the state of the art.
Vehicle collisions represent a significant public health hazard as well as a cause of significant economic loss each year. Therefore, there has been a long felt need for an inexpensive collision avoidance system for use in aircraft, automobiles and other vehicles.
Recently.sup.(1), the National Highway Traffic Safety Administration (NHTSA) identified autonomous intelligent cruise control (AICC) and similar autonomous collision avoidance systems (CAS) as precursors to fully automated driving in the proposed future Automated Highway System. The spring 1994 issue of IVHS Review.sup.(2) indicates that the significance of highway safety as a public health hazard is greatly underestimated. Highway collisions are the sixth leading cause of death in the USA, and the major cause of death for people below the age of 25. A recent NHTSA report gives the costs associated with the 44,531 deaths, 5.4 million injuries, and 28 million damaged vehicles in 1990; the losses are estimated to be $137.5 billion in lost wages and other direct costs. The economic loss from traffic collisions represents greater than 2% of the U.S. GNP, and results in nearly 2 billion hours of lost time and 7.5 million liters of wasted fuel each year.
Collision avoidance systems for highway vehicles are designed to be a countermeasure to one or more classes of recognized collision types. Collision avoidance systems for highway vehicles are generally grouped into three categories: near obstacle detection systems (NODs), forward looking (FLR) systems, and wide angle imaging systems for all weather and night vision (AWNV).
The clear choice of wavelength for FLR and AWNV sensors is the millimeter wavelength (MMW) range. The European frequency allocation is 76 to 77 GHz. The Japanese frequency allocation is currently 59 to 60 Ghz, and the U.S. allocation, while still under discussion, has tended to be around 76 to 77 GHz, although 94 GHz
is also discussed. The electronic and signal processing parts of FLR and AWNV systems are considered to be essentially developed and ready for mass production.
Millimeter wavelength transceiver electronic packages for use in conjunction with vehicle collision avoidance systems for vehicles such as, for example aircraft, are already commercially available. An example of such a commercially available transceiver electronic package is Litton's millimeter wavelength transceiver..sup.(4)
However, an inexpensive scannable millimeter wavelength antenna is not yet commercially available for use with such collision avoidance systems. As a practical economic matter, the phase shifting element solution used for prior art seeker applications cannot be adopted for use in a commercial vehicle collision avoidance system because of the extremely high cost of the individual phase shifting elements that are a part of such seeker applications, (i.e., from approximately $2,000 to approximately $10,000). Further, the phase shifting element solution used for prior art seeker applications cannot be adopted for use in a commercial vehicle collision avoidance system because of the very high cost of the skilled hand labor required for the assembly of such a phased array antenna.
An IEEE workshop in May 1994.sup.(3) on millimeter wavelength technology for automobiles identified the millimeter wavelength scanning antenna as a key element needed to complete an economically feasible automobile collision avoidance system for automobiles. However, of more than 30 existing antenna technologies previously studied, none satisfies the full range of required parameters for such a millimeter wavelength scanning antenna, especially the possibility of being mass produced at very low cost.
A millimeter wavelength scanning antenna that is economically feasible for use in automobiles would probably be feasible for use in more expensive vehicles such as, for example, aircraft. A commonly accepted cost of an economically feasible forward looking millimeter wavelength antenna for an automobile is approximately $50. Clearly, the existing antennas that are widely used for prior art seeker applications cannot be manufactured at such a low cost. Therefore, there has been a long felt need for a low cost millimeter wavelength scanning antenna.
The availability of a low cost millimeter wavelength scanning antenna would make an inexpensive vehicle collision avoidance system a commercial reality. Such a low cost millimeter wavelength scanning antenna could be used to provide an inexpensive collision avoidance system for aircraft, automobiles or other types of vehicles.
The below-referenced U.S. patent discloses embodiments that are satisfactory for the purposes for which they were intended but which have certain disadvantages. The disclosure of the below-referenced prior United States patent in its entirety is hereby expressly incorporated by reference into the present application.
U.S. Pat. No. 5,305,123 discloses a light controlled spatial and angular electromagnetic wave modulator. In embodiments disclosed in the above-referenced prior patent, periodic perturbations of the complex dielectric field in the surface of the semiconductor material induced by an optical control pattern cause electromagnetic
waves to be coupled out-of a semiconductive material in a particular direction depending upon the period of the perturbations. Further, rapid variations in the period of the perturbations can be induced by controlling the optical control pattern. Furthermore, rapidly changing the period of the perturbations, (i.e., the grating period induced by the optical control pattern), can be used to control the direction of beam scanning and beam steering.
A disadvantage of embodiments disclosed in the above-referenced prior patent is that the millimeter wavelength energy propagates though the control pattern reactive semiconductive plate. Another disadvantage of preferred embodiments disclosed in the above-referenced prior patent is that a separate optical control pattern is directed onto the semiconductive plate to steer the beam with the attendant complexity and cost associated with generating and directing such an optical control pattern.